Switching of PVC connection

ABSTRACT

The invention provides a PVC switching control method for an ATM communication network which allows high speed changeover of a connection upon occurrence of/release from a trouble and is superior in reliability and maintenance facility and simple in control. A master PVC connection and an OAM connection are set between two ATM exchanges, and a bypassing PVC connection and an OAM connection prepared in advance for bypassing are set between the two ATM exchanges. If occurrence of/release from a trouble with and of the master PVC connection is recognized by the ATM exchanges using an OAM function, then the operative PVC connection is switched between the master PVC connection and the bypassing PVC connection.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a network management technique, and moreparticularly to an ATM (Asynchronous Transfer Mode) exchange system anda switching control method for a permanent virtual connection(hereinafter referred to as “PVC connection”) for an ATM network.

2. Description of the Related Art

As diversification, increase in speed and increase in capacity ofservices in an ATM network in recent years proceed, it becomes asignificant subject to improve an ATM exchange system in terms of theperformance, function and reliability. As a necessary function, it isdemanded particularly to augment the reliability of a PVC connection.Specifically, when a trouble occurs with a circuit, it is significant tocontinue communication of a PVC connection with a minimum cell loss.

As a method of preventing disconnection of a PVC connection by a troubleof a circuit or an apparatus, it is a possible idea to employ aredundant configuration (dual configuration, n+1 multiple configuration)in hardware for a circuit itself. This method, however, isdisadvantageous in that it requires complicated maintenance.

As another method, it is known to use a network management system (NMS)to automatically or manually switch, when a trouble occurs with a PVCconnection, the PVC connection to another PVC connection of anotherroute (refer to, for example, Japanese Patent Laid-Open No. 2000-59374).With the method, however, when a trouble occurs or upon release from atrouble, it is necessary for the network management system to notifyeach ATM exchange of setting/deletion of a PVC connection. Therefore,the method has a problem in that considerable time is required for theexchanging process. Further, if a trouble occurs with the networkmanagement system, then this makes setting itself of a PVC connectionimpossible.

Thus, a method has been proposed wherein network management is performedautonomously and discretely without depending upon a network managementsystem. For example, Japanese Patent Laid-Open No. 266480/1997 disclosesa method wherein, when a trouble occurs with a circuit, a routingfunction of a switched virtual connection (SVC) is used to set abypassing SVC connection.

Meanwhile, Japanese Patent Laid-Open No. 215148/1999 discloses anothermethod wherein both of a PVC connection and an SVC connection are usedsuch that, if a trouble occurs with the PVC, a call setting procedure bythe SVC is executed to set an optimum SVC connection as a bypass link.

However, with the conventional autonomous PVC bypassing method, however,when a trouble occurs with a currently used PVC connection, a bypassingSVC connection is searched for and set. Therefore, rapid switchingcannot be anticipated. Further, although a bypassing connection is setand switchably used when a trouble occurs with a currently usedconnection and then the bypassing connection is disconnected and thecurrently used connection is switchably used upon release of thecurrently used connection, the conventional autonomous PVC bypassingmethod does not propose any autonomous countermeasure of softwareagainst occurrence of/release from a trouble which may occur with thecurrently used or bypassing connection.

SUMMARY OF THE INVENTION

An aspect of the present invention is directed to providing a PVCswitching control method which allows high speed changeover of aconnection upon occurrence of/release from a trouble and is superior inreliability and maintenance facility and simple in control.

According to an aspect of the present invention, there is provided a PVCswitching control method for controlling a PVC connection in an ATMcommunication network, comprising the steps of setting a plurality ofPVC connections and individually corresponding controlling connectionsbetween two ATM exchanges of the ATM communication network, anddetecting, by each of the ATM exchanges, occurrence of and release froma trouble with and of a PVC connection corresponding to any of thecontrolling connections and switching an operative PVC connection toanother one of the PVC connections in response to a result of thedetection.

The PVC switching control method may be configured such that, if, whileone of the PVC connections is used as the currently used PVC connection,it is detected from the corresponding controlling connection that atrouble has occurred with the PVC connection, then each of the ATMexchanges switches the operative PVC connection to another one of thePVC connections as a bypassing PVC connection. Further, the PVCswitching control method may be configured such that, if, while thebypassing PVC connection is used, it is detected that the currently usedPVC connection has been released through the corresponding controllingconnection, then each of the ATM exchanges switches the operative PVCconnection to the currently used PVC connection.

The controlling connections may be set by an operation administrationand maintenance (OAM) function. Further, each of the ATM exchanges maydetect a trouble through the fact that an alarm indication signal cellof the operation administration and maintenance function is inputtedthereto or through the fact that a continuity check cell of theoperation administration and maintenance function is not inputtedthereto.

According to another aspect of the present invention, there is provideda PVC switching control method for controlling a PVC connection in anATM communication network, comprising the steps of setting a master PVCconnection and a master side operation administration and maintenanceconnection corresponding to the master PVC connection between a firstATM exchange and a second ATM exchange, setting a bypassing PVCconnection prepared in advance for bypassing of the master PVCconnection and a bypassing side operation administration and maintenanceconnection corresponding to the bypassing PVC connection between thefirst and second ATM exchanges, and switching, if both of the first andsecond ATM exchanges detect a trouble of the master PVC connectionthrough the master side operation administration and maintenanceconnection, the PVC connection to the bypassing PVC connection by meansof the first and second ATM exchanges.

The PVC switching control method may be configured such that, if, whilethe first and second ATM exchanges use the bypassing PVC connection, thefirst and second ATM exchanges detect a release of the master PVCconnection through the master side OAM connection, each of the first andsecond ATM exchanges switches the PVC connection to the master PVCconnection.

The PVC switching control method may be configured such that a pluralityof repeating ATM exchanges are connected on a route of the bypassing PVCconnection and a connection for forming the bypassing PVC connection isset in each of the repeating ATM exchanges. In this instance, each ofthe first and second ATM exchanges may designate the connection set inadvance and signal an ATM cell to a neighboring one of the plurality ofrepeating ATM exchanges through the designated connection.

In summary, according to the PVC switching control methods for an ATMcommunication network, a master PVC connection and an operationadministration and maintenance connection corresponding to the PVCconnection are set between two ATM exchanges, and a bypassing PVCconnection and an operation administration and maintenance connectionprepared in advance for bypassing are set between the two ATM exchanges.Occurrence of and release from a trouble with and of the master PVCconnection can be detected through the operation administration andmaintenance connection, and autonomous and high speed switching betweenthe master PVC connection and the bypassing PVC connection can beachieved. Since such detection and switching as described above do notrely upon control of a network management system, the switching speed ofthe PVC connection can be augmented, and the cell loss is reduced andthe reliability of the PVC connection is augmented.

Also where three or more PVC connections are set between two stations ofan ATM communication network, switching between PVC connections andswitching back between the PVC connections can be executed by controlfor a single apparatus. Therefore, the control is simplified. Further,when a trouble occurs with and/or is eliminated from a circuit, anetwork manager need not perform PVC connection setting again.Therefore, maintenance is facilitated.

The above and other aspects, features and advantages of the presentinvention will become apparent from the following description and theappended claims, taken in conjunction with the accompanying drawings inwhich like parts or elements are denoted by like reference symbols.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a block diagram showing an ATM network configuration towhich a PVC switching control method according to the present inventionis applied;

FIG. 1 b is a schematic view of an ATM exchange showing a master andbypassing connection group (PVC group) in an ATM exchange at aterminating portion of a PVC connection;

FIG. 2 is a block diagram of an ATM network showing a flow of an ATMcell during normal operation of the ATM network shown in FIG. 1 a;

FIG. 3 is a block diagram of the ATM network configuration of FIG. 1 ashowing a flow of an ATM cell when a trouble occurs with a master PVCconnection;

FIG. 4 is a flow diagram illustrating a status transition of a PVCswitching function of the ATM network configuration of FIG. 1 a;

FIG. 5 is a block diagram of another ATM network showing a flow of anATM cell during normal operation; and

FIG. 6 is a similar view but illustrating a flow of an ATM cell when atrouble occurs with a master PVC connection in the ATM network of FIG.5.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 a shows an ATM network configuration to which a PVC switchingcontrol method according to the present invention is applied, and FIG. 1b shows an ATM exchange and illustrates a master and bypassingconnection group (PVC group) in an ATM exchange at a terminating portionof a PVC connection. The PVC group includes a master PVC connection, amaster side OAM connection, a bypassing side PVC connection and abypassing side OAM connection.

In the present embodiment, in order to simplify description, it isassumed that the ATM network includes ATM exchanges 1 to 6 and currentlyused and bypassing PVC connections are set between the ATM exchange 1and the ATM exchange 4. Further, each of the ATM exchanges 1 to 6 isprovided with an OAM function and can supervise an AIS (Alarm IndicationSignal) cell and/or a CC (Continuity Check) cell.

In particular, a master connection group 101 including a PVC connection103 and an OAM connection 104 are set bidirectionally in a route fromthe ATM exchange 1 to the ATM exchange 4 through the ATM exchange 2 andthe ATM exchange 3. Further, a bypassing connection group 102 includinga PVC connection 105 and an OAM connection 106 is set in another routefrom the ATM exchange 1 to the ATM exchange 4 through the ATM exchange 5and the ATM exchange 6 thereby to form a bypass path to be used when atrouble occurs with the master connection.

Referring to FIG. 1 b, in each of the ATM exchanges 1 and 4, traffic andVPI/VCI corresponding to a PVC set are reserved in advance.Consequently, when occurrence of/release from a trouble is detected byan OAM connection, PVC switching can be performed immediately.

Each of the ATM exchanges 1 and 4 which are terminations of the masterconnection group 101 and the bypassing connection group 102,respectively, can utilize an OAM function to detect occurrence of atrouble with a corresponding PVC connection and switch, when a troubleoccurs, the PVC connection at a high speed to the other PVC connection.A trouble occurring with a PVC connection can be detected by monitoringan AIS cell and/or a CC cell by the OAM function by means of the ATMexchanges 1 and 4.

In this manner, in the ATM network according to the present embodiment,the connections 104 and 106 for a controlling OAM are extended for themaster PVC connection 103 and the bypassing PVC connection 105,respectively. In the following, operation of the ATM network isdescribed.

(Operation)

FIG. 2 illustrates a flow of an ATM cell in the ATM network of FIG. 1when the ATM network operates normally. Referring to FIG. 2, while thenetwork operates normally, the master PVC connection group 101 is usedfor communication, and the ATM exchange 1 and the ATM exchange 4supervise to discriminate whether or not an AIS cell is inputted tonormally confirm whether or not the master PVC connection 103 is normal.However, it is otherwise possible to supervise for a CC cell of the OAMfunction to confirm that the PVC connection 103 is normal.

FIG. 3 shows a flow of an ATM cell in the ATM network when a troubleoccurs with the master PVC connection. Referring to FIG. 3, if a trouble301 occurs with a transmission line of the ATM exchanges 2 and 3 on theroute of the master PVC connection, then the ATM exchange 1 and the ATMexchange 4 recognize the occurrence of the trouble 301 from an AIS/CCcell of the OAM function and change over the PVC connection from themaster PVC connection 103 to the bypass PVC connection 105.

In this manner, even if a trouble occurs with the route of the masterPVC connection 103, the PVC communication can be continued withoutinterruption through the bypass PVC connection 105 which bypasses thetrouble 301. In this instance, since the OAM connection 106 is extendedto the bypass PVC connection 105, similar detection of occurrenceof/release from a trouble can be performed.

If the trouble of the master PVC connection is eliminated after theswitching to the PVC connection 105, then since the ATM exchange 1 andthe ATM exchange 4 can recognize this using the OAM function thereof,the PVC connection can be switched from the bypass PVC connection 105 tothe master PVC connection 103 automatically.

FIG. 4 illustrates a status transition of the PVC switching function ofthe ATM network. Referring to FIG. 4, reference numerals (1) to (6)represent occasions at which a status transition occurs, and (1)represents a trouble with the master connection, (2) a trouble with thebypassing connection, (3) a release of the master connection, (4) arelease of the bypassing connection, (5) manual switching, and (6)manual release.

A [status S1] represents an ordinary state wherein the network isoperating normally and the master and bypassing connections are normalwhile the master connection is currently used. In this state, both ofmanual switching and automatic switching upon occurrence of a troublewith the master connection are possible.

A [status S2] represents a state wherein both of the master andbypassing connections are normal and the bypassing connection iscurrently used. In this state, both of manual release and automaticswitching upon occurrence of a trouble with the master connection arepossible.

A [status S3] represents a state wherein a trouble has occurred with themaster connection and the bypassing connection is currently used. Bothof manual release and automatic switching upon occurrence of a troublewith the bypassing connection are impossible.

A [status S4] represents a state wherein a trouble has occurred with thebypassing connection and the master connection is currently used. Bothof manual switching and automatic switching upon occurrence of a troublewith the master connection are impossible.

A [status S5] represents a state wherein a trouble has occurred alsowith the master connection which was normal and both of the master andbypassing connections are in trouble. In this state, manual switching isimpossible. If the trouble of the bypassing connection is eliminated(occasion (4)), then automatic switching is performed to establish thestatus S3 wherein the bypassing connection is used. If the masterconnection is released (occasion (3)), then automatic switching isperformed to establish the status S4 wherein the master connection isused.

A [status S6] represents a state wherein a trouble has occurred alsowith the bypassing connection which was normal and both of the masterand bypassing connections are in trouble. In this state, manual releasecan not be performed. If the master connection is released (occasion(3)), then automatic switching is performed to establish the status S4wherein the master connection is used. Also when the trouble of thebypassing connection is eliminated (occasion (4)), automatic switchingis performed to establish the status S3 wherein the bypassing connectionis used.

In this manner, in the ATM network described above, augmentation of afunction of a PVC connection provided by an ATM exchange by software canbe anticipated. The following three advantages are anticipated with thepresent embodiment. (1) Since an NMS need not be used to notify each ATMexchange of setting/deletion of a PVC connection, the changeover speedof a PVC connection is high, and the reliability of the PVC connectionis improved. (2) Even where a plurality of PVC connections are setbetween two ATM exchanges, processes for switching and switching backbetween PVC connections can be performed by control for a singleapparatus and therefore are simplified. (3) Upon occurrence of/releasefrom a trouble with a circuit, the network manager need not performsetting for a PVC connection again.

FIG. 5 shows a configuration of an ATM network and illustrating a flowof an ATM cell in normal operation according to another embodiment ofthe present invention. FIG. 6 illustrates a flow of an ATM cell when atrouble occurs with a master PVC connection in the ATM network.

In the present embodiment, in order to simplify description, it isassumed that the ATM network includes ATM exchanges 10 to 60 andcurrently used and bypassing PVC connections are set between the ATMexchange 10 and the ATM exchange 40. Further, similarly as in the firstembodiment described hereinabove, each of the ATM exchanges 10 to 60 isprovided with an OAM function and can supervise an AIS (Alarm IndicationSignal) cell and/or a CC (Continuity Check) cell.

In a normal operation state of the ATM network, bypassing connections501 and 502 are extended between the ATM exchanges 50 and 60 in thebypass route. More particularly, traffic and VPI/VCI corresponding tothe PVC group to be protected are reserved for the bypassing connections501 and 502 in the ATM exchanges 50 and 60 as seen in FIG. 1 b.

If a trouble occurs with the master PVC connection, then the ATMexchanges 10 and 40 switch the PVC connection from the master PVCconnection to the bypass PVC connection as described above. In thisinstance, however, the ATM exchange 10 designates the bypassingconnection 501 and transmits an ATM cell to the neighboring ATM exchange50 through the bypassing connection 501. Similarly, also the ATMexchange 40 designates the bypassing connection 502 and transmits an ATMcell to the neighboring ATM exchange 60 through the bypassing connection502. Consequently, further rapid PVC switching control can be performed.

It is to be noted that, while, in the embodiments described above, tworepeating exchanges are involved, the foregoing description similarlyapplies also where three or more repeating exchanges are involved.

While preferred embodiments of the present invention have been describedusing specific terms, such description is for illustrative purposesonly, and it is to be understood that changes and variations may be madewithout departing from the spirit or scope of the following claims.

1. A PVC switching control method for controlling a PVC connection in acommunication network, comprising: setting a plurality of PVCconnections and individually corresponding controlling connectionsbetween two exchanges of the communication network; detecting, by eachof the exchanges, occurrence of or release from trouble with a PVCconnection through the corresponding controlling connection; andswitching an operative PVC connection to another one of the PVCconnections in response to a result of the detection.
 2. The PVCswitching control method as claimed in claim 1, wherein, if, while oneof the PVC connections is used as a currently used PVC connection, it isdetected from the corresponding controlling connection that trouble hasoccurred with the currently used PVC connection, then each of theexchanges switches the operative PVC connection to another one of thePVC connections as a bypassing PVC connection.
 3. The PVC switchingcontrol method as claimed in claim 2, wherein, if, while the bypassingPVC connection is used, it is detected that the currently used PVCconnection has been released through the corresponding controllingconnection, then each of the exchanges switches the operative PVCconnection to the currently used PVC connection.
 4. The PVC switchingcontrol method as claimed in claim 1, wherein the controllingconnections are set by an operation administration and maintenancefunction.
 5. The PVC switching control method as claimed in claim 4,wherein each of the exchanges detects trouble through receipt of analarm indication signal cell from the operation administration andmaintenance function over one of the controlling connections.
 6. The PVCswitching control method as claimed in claim 4, wherein each of theexchanges detects trouble through failure to receive a continuity checkcell from the operation administration and maintenance function over oneof the controlling connections.
 7. A PVC switching control method forcontrolling a PVC connection in a communication network, comprising:setting a master PVC connection and a master side operationadministration and maintenance (OAM) connection corresponding to themaster PVC connection between a first exchange and a second exchange;setting a bypassing PVC connection prepared in advance for bypassing ofthe master PVC connection and a bypassing side OAM connectioncorresponding to the bypassing PVC connection between the first andsecond exchanges; and switching, if both of the first and secondexchanges detect trouble of the master PVC connection through the masterside OAM connection, the master PVC connection to the bypassing PVCconnection at the first and second exchanges.
 8. The PVC switchingcontrol method as claimed in claim 7, wherein, if, while the first andsecond exchanges use the bypassing PVC connection, the first and secondexchanges detect a release of the master PVC connection through themaster side OAM connection, each of the first and second exchangesswitches the PVC connection to the master PVC connection.
 9. The PVCswitching control method as claimed in claim 7, wherein a plurality ofrepeating exchanges are connected on a route of the bypassing PVCconnection and a connection for forming the bypassing PVC connection isset in each of the repeating exchanges.
 10. The PVC switching controlmethod as claimed in claim 9, wherein each of the first and secondexchanges designates a connection set in advance and signals a cell to aneighboring one of the plurality of repeating exchanges through thedesignated connection.
 11. A PVC switching control system forcontrolling a PVC connection in a communication network, comprising:means for setting a plurality of PVC connections and correspondingcontrolling connections between first and second exchanges of thecommunication network; means for detecting, by each of the first andsecond exchanges, occurrence of or release from trouble with a PVCconnection based on information from the corresponding controllingconnection; and means for switching an operative PVC connection toanother one of the PVC connections in response to a result of thedetection.
 12. The PVC switching control system of claim 11, wherein thecontrolling connections include operation administration and maintenance(OAM) connections to provide one of an alarm signal or a continuitycheck signal.
 13. The PVC switching control system of claim 11, wherein,if, while one of the PVC connections is used as a currently used PVCconnection, it is detected from the corresponding controlling connectionthat trouble has occurred with the currently used PVC connection, theneach of the first and second exchanges switches the operative PVCconnection to another one of the PVC connections as a bypassing PVCconnection.
 14. The PVC switching control system of claim 13, wherein,if, while the bypassing PVC connection is used, it is detected that thecurrently used PVC connection has been released through thecorresponding controlling connection, then each of the first and secondexchanges switches the operative PVC connection to the currently usedPVC connection.
 15. The PVC switching control system of claim 11,wherein the controlling connections are set by an operationadministration and maintenance (OAM) function.
 16. The PVC switchingcontrol system of claim 15, wherein each of the first and secondexchanges detects trouble via receipt of an alarm indication signal cellfrom the OAM function over one of the controlling connections.
 17. ThePVC switching control system of claim 15, wherein each of the first andsecond exchanges detects trouble via failure to receive a continuitycheck cell from the OAM function over one of the controllingconnections.
 18. A first exchange in a network, comprising: means forsetting a master PVC connection and a master side operationadministration and maintenance (OAM) connection corresponding to themaster PVC connection between the first exchange and a second exchange;means for setting a bypassing PVC connection prepared in advance forbypassing of the master PVC connection and a bypassing side OAMconnection corresponding to the bypassing PVC connection between thefirst and second exchanges; means for detecting trouble of the masterPVC connection through the master side OAM connection; and means forswitching the master PVC connection to the bypassing PVC connection iftrouble of the master PVC connection is detected.